After oil and gas wells have been abandoned after production has ceased, the wells must be properly capped to both return the land where the well is located to its previous state as well as provide a safe and stable cap to the well that minimizes risk to the land owner's subsequent use of their land as well as minimizing risk to personnel who may in the future re-enter the well. The abandoned wells are generally capped by an oil and gas company, licensee or well abandonment service provider.
Regulations in many jurisdictions generally require that in capping an abandoned well that the production and surface casings of the well be trimmed approximately 1 m below the ground surface and a simple steel plate cover system attached to the well casings. As shown in FIG. 1, simple steel covers are welded to the production casing 10 and surface casing 12 using tack welds or a continuous fillet weld 14. In each case, steel plate (typically ½″) 16, 18 is usually welded to the inside of surface and production casing after the upper 1 m of each casing has been trimmed to a height approximately 1 m below the ground surface.
Unfortunately, the typical oilfield capping system has no allowance for the escape of heated gases during the capping welding process other than where the plate is being welded to the casing. In addition, there is no allowance for the escape of heated or accumulated formation gases upon re-entry of the well without hot tapping. These limitations lead to serious safety risks both during abandonment and/or re-entry.
For example, in approximately 90% of those wells that are ultimately re-entered, modest levels of formation gas will be found to be leaking at the location where the steel plates are attached to the well casing. This leaking gas which passes through the fine pores of the weld is very difficult to detect and provides limited or no information about the composition and/or backside pressure within either the production or surface casing of the well.
Moreover, the current methodologies of capping a well are problematic in a number of ways from a safety and functional perspective. Most importantly, for those wells that have been capped using a continuous fillet weld that fully seals the well, there is a risk of a significant gas pressure build-up within the well such that the procedures to re-enter the well must properly and efficiently release any pressure build-up without risk to personnel. As a result, protocols for re-entering a well are unnecessarily complex for those situations where there is limited or no safety risk but are required to ensure safety for the potentially dangerous situation. In other words, in each case, there is no provision to determine the gas composition and/or rate of leak.
In the case of cap plates that are tack-welded in place, while the unsealed weld may allow gas to dissipate, ground water may leak into the well. Groundwater is un-inhibited and rich in oxygen and micro-organisms; causing the acceleration of internal corrosion.
Moreover, the procedures to install steel cap plates are very inefficient and may not provide the effective sealing. Typically, service personnel will crudely torch cut a cap plate at the site on the back of a welding truck in an uncontrolled environment thus producing an imperfect circle that is used as the capping plate. Imperfect circles will contribute to inferior welds.
As a result, there has been a need for a system and method that addresses the above problems and more specifically provides a system that provides an effective seal to both production and surface casing, that prevents ground water contamination from entering the production and surface casing whilst allowing the release of gas from the system in a controlled manner. In addition, there has been a need for a method of abandoning a well that improves the efficiency of the at-site procedure as well as any subsequent re-entry of the well. Further still, there has been a need for a system that simplifies the re-entry protocols while enhancing the efficiency of hydrostatically killing a well if necessary.
A review of the prior art reveals that such a system has not been provided.